Does anyone know why my 2nd conditional statement is being ignored in this while loop?

Does anyone know why my second conditional statement "units(1) ~= 'n'" is being ignored when this code block is run? When the 2nd statement is removed the code runs without problems.

   units = strings([1,4]);

   torque_force_input = input('Input the unit of force for your initial torque\n','s');
   units(1)= torque_force_input;
    
   while units(1) ~= 'N'||units(1) ~= 'n'
        disp('Please input a valid unit for the torque''s force.');
        torque_force_input = input('Input a unit of force for your torque...\n','s');
        units(1)= torque_force_input;
       
    end 

[Stephen23]

Given A~=B, can you think of a single value of X which will make this statement false?:

X~=A || X~=B

Answer 1

[Mehmed Saad]

Suppose i enter Nm in command window then units will be

units

units = 

  1×4 string array

    "Nm"    ""    ""    ""

if you try the access the first letter

units(1)
ans = 

    "Nm"

you have the complete word the user enters and not a single character

to access first index

units{1}(1)
ans =

    'N'

Now for the while loop, it keeps runing untill it receives false. so if user inputs N, so

    'N' ~= 'N' || 'N' ~= 'n'

this will give you true and while loop will keep runing. you need a condition such that if any of them is true you get false and if both are false you get true